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Testosterone Replacement, Low T, HCG, & Beyond
Blood Test Discussion
Calculate Free Testosterone with TruT by FPT
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<blockquote data-quote="tareload" data-source="post: 189496"><p>Maybe this will help...</p><p>[URL unfurl="true"]https://en.m.wikipedia.org/wiki/Observational_error[/URL]</p><p>[URL unfurl="true"]http://www2.ece.rochester.edu/courses/ECE111/error_uncertainty.pdf[/URL]</p><p></p><p></p><p>There’s error involved in any measurement. Your conflating direct RIA free T methods which measure some quantity that may correlate with absolute free T (a proxy for free T) and dialysis free T method which attempts to measure actual free T.</p><p></p><p>Just because there is error involved in any measurement doesn’t mean the assay isn’t measuring the absolute quantity (or at least attempting to). There is no proxy variable involved with equilibrium dialysis coupled with LCMS/MS measurement of free T. There is a proxy variable involved with direct RIA free T measurement. All of this is academic but important to differentiate.</p><p></p><p>Also the best fit linear regression line in the plot above does not indicate that the API4000 measurement is consistently 32% higher that the reference lab. Clearly the Bland Altman bias plot shows this is far from the case. Instead what the ordinary least squares regression slope indicates is that the best fit line that minimizes the SSE (between the two method measurements in this study) has a slope of 1.32 (which assumes no error in the reference method). This can be affected by high leverage points / outliers, blah blah.</p><p></p><p>More info if you’d like:</p><p>[URL unfurl="true"]https://online.stat.psu.edu/stat462/node/170/[/URL]</p><p>[URL unfurl="true"]https://en.m.wikipedia.org/wiki/Bland–Altman_plot[/URL]</p><p></p><p>I showed yesterday in this thread that Vermeulen method was within approx. 20% of one of your dialysis free T results. Tru-T method way WAY overestimates (over 100%).</p><p></p><p>Respectfully, with your logic, when I take out a micrometer and measure the thickness of a sheet of paper I am not actually measuring the thickness of the sheet of paper but only a proxy. You are confusing proxy variable error with measurement error. If one day it is proven that free T does not exist (<a href="https://pubmed.ncbi.nlm.nih.gov/2673754/" target="_blank">free hormone hypothesis</a> would be disproven) and is not measurable, then I’ll buy your statement that dialysis + LCMS/MS is only a proxy for free T.</p><p></p><p>Make sense? We aren’t there yet, and our understanding of the physics of the situation indicates we can measure absolute free T (of course with the measurement error that comes along for the ride).</p><p></p><p>I now end my statistics lecture.</p></blockquote><p></p>
[QUOTE="tareload, post: 189496"] Maybe this will help... [URL unfurl="true"]https://en.m.wikipedia.org/wiki/Observational_error[/URL] [URL unfurl="true"]http://www2.ece.rochester.edu/courses/ECE111/error_uncertainty.pdf[/URL] There’s error involved in any measurement. Your conflating direct RIA free T methods which measure some quantity that may correlate with absolute free T (a proxy for free T) and dialysis free T method which attempts to measure actual free T. Just because there is error involved in any measurement doesn’t mean the assay isn’t measuring the absolute quantity (or at least attempting to). There is no proxy variable involved with equilibrium dialysis coupled with LCMS/MS measurement of free T. There is a proxy variable involved with direct RIA free T measurement. All of this is academic but important to differentiate. Also the best fit linear regression line in the plot above does not indicate that the API4000 measurement is consistently 32% higher that the reference lab. Clearly the Bland Altman bias plot shows this is far from the case. Instead what the ordinary least squares regression slope indicates is that the best fit line that minimizes the SSE (between the two method measurements in this study) has a slope of 1.32 (which assumes no error in the reference method). This can be affected by high leverage points / outliers, blah blah. More info if you’d like: [URL unfurl="true"]https://online.stat.psu.edu/stat462/node/170/[/URL] [URL unfurl="true"]https://en.m.wikipedia.org/wiki/Bland–Altman_plot[/URL] I showed yesterday in this thread that Vermeulen method was within approx. 20% of one of your dialysis free T results. Tru-T method way WAY overestimates (over 100%). Respectfully, with your logic, when I take out a micrometer and measure the thickness of a sheet of paper I am not actually measuring the thickness of the sheet of paper but only a proxy. You are confusing proxy variable error with measurement error. If one day it is proven that free T does not exist ([URL='https://pubmed.ncbi.nlm.nih.gov/2673754/']free hormone hypothesis[/URL] would be disproven) and is not measurable, then I’ll buy your statement that dialysis + LCMS/MS is only a proxy for free T. Make sense? We aren’t there yet, and our understanding of the physics of the situation indicates we can measure absolute free T (of course with the measurement error that comes along for the ride). I now end my statistics lecture. [/QUOTE]
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Testosterone Replacement, Low T, HCG, & Beyond
Blood Test Discussion
Calculate Free Testosterone with TruT by FPT
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